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EDMUND G.SkowN JA. <br /> �� U[NfRNOfl <br /> CEIIORNi• MA�nf HEW ROD IO.EZ <br /> Water Boards [NV RORMINIK PkprFCI,ON <br /> Central Valley Regional Water Quality Control Board <br /> 9 May 2018 <br /> Randy Coil <br /> Atlantic Richfield Company <br /> 501 Westlake Park Boulevard, WL1-28.16B <br /> Houston, TX 77079 <br /> FORMER ARCO STATION #6100, 25775 S. PATTERSON PASS ROAD, TRACY, SAN <br /> JOAQUIN COUNTY, CASE# 390265 <br /> Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br /> reviewed the Semi-Annual Groundwater Monitoring and Remediation Progress Report, Fourth <br /> Quarter 2017 and First Quarter 2018 (Report) dated 30 April 2018, submitted on your behalf by <br /> Arcadis U.S. Inc. (Arcadis) for the Former ARCO Station #6100 unauthorized petroleum release <br /> at 25775 S. Patterson Pass Road in Tracy (Site). In the Report, Arcadis details the 4th quarter <br /> 2017 and 1St quarter 2018 remedial system operation and maintenance (O&M) activities and 1St <br /> quarter 2018 groundwater sampling activities, and the resultant findings. In the Report, Arcadis <br /> recommends ceasing operation of the soil vapor extraction and air-sparge (SVE/AS) remedial <br /> system. <br /> As of 28 April 2018, the SVE/AS system has removed a total of 193,824 pounds of <br /> hydrocarbons since May 2005. The average mass removal rate during April 2018 was <br /> approximately 2.5 pounds per day. While recent increases in mass removal rate have occurred <br /> during rebound testing, removal rates quickly decreased following system re-start. Central <br /> Valley Water Board staff concurs with Arcadis's recommendation to cease system operation. <br /> In their Revised Work Plan dated 19 May 2017, Arcadis proposed the following scope of work at <br /> the Site: <br /> Boring Location Total Depth Soil Sampling Depth Analysis <br /> (ft b s (ft b s <br /> B-49 Near EW-3 <br /> B-50 Near VW-1 <br /> B-51 Near MW-15 70 2.5, 5ft intervals <br /> B-52 Near VW-16 from 5ft to TDA GRD, BTEX, MTBE <br /> B-53 Near BS-9 <br /> B-54 Near L2-1-2.5 2.5 2.5 <br /> B-55 Near Former 6 6 GRO, DRO, TOG, VOCs, SVOCs, <br /> B-56 WOT 13 13 PCBs, Title 22 metals <br /> B-57 NE corner 13 6, 13 Title 22 metals <br /> GRO=gasoline range organics, DRO-diesel range organics,BTEX=benzene,toluene,ethylbenzene,xylenes;TOG-total oil and <br /> grease;VOCs=volatile organic compounds;SVOCs=semi-VOCs;PCBs=polychlorinated biphenyls;TD=total depth;WOT=waste <br /> oil tank;NE=northeast;ft bgs=feet below ground surface <br /> A=Soil samples submitted to lab will be selected based on PID field screening <br /> (CARL E. LONGLEY SCD, P.E.,CHAIR I PAMELA C. CREEOON P.E., BCEE, EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200.Rancho Cordova,CA 98870 1 www.waterboarde.ca.0ov/centralvalley <br /> IRECYGIED PAPER <br />